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      • KCI등재

        PCT Curve and Cycling Performance of MgH2-Ni-NaAlH4-Ti Alloy Milled under H2

        송명엽,이성호,곽영준,박혜령 대한금속·재료학회 2014 대한금속·재료학회지 Vol.52 No.5

        In this study, MgH2 was used as a starting material instead of Mg. A sample with a compositionof 86 wt% MgH2-10 wt% Ni-2 wt% NaAlH4-2 wt% Ti (designated MgH2-10Ni-2NaAlH4-2Ti) was prepared byreactive mechanical grinding. Its Pressure-Composition-Temperature (PCT) curve measurement, hydridingdehydridingcycling performance measurement, and microstructure observation were then performed. Thedesorption PCT curve at 593 K for MgH2-10Ni-2NaAlH4-2Ti at the first cycle exhibited a long plateau ataround 2.6 bar, and a short plateau at about 3.6 bar, which correspond to equilibrium plateau pressures ofMg-H and Mg2Ni-H systems, respectively. The hydriding rate at 593 K under 12 bar H2 increased as thenumber of cycles, n, increased from 1 to 4, and it decreased from n=4 to n=15. At n=14, MgH2-10Ni-2NaAlH4-2Ti absorbed 3.02 wt% H for 2.5 min, 3.36 wt% H for 5 min, 3.51 wt% H for 10 min, and 3.58 wt% H for 30min, which is 93.0% of the hydrogen absorbed for 30 min at n=4.

      • KCI등재

        Phase Transformations and Hydrogen-Storage Characteristics of Mg-Transition Metal-Oxide Alloys

        송명엽,Sung Hwan Baek,Jean-Loius Bobet,박혜령 대한금속·재료학회 2013 METALS AND MATERIALS International Vol.19 No.2

        Samples with the compositions of 76.5 wt%Mg-23.5 wt%Ni (Mg-Ni), 71.5 wt%Mg-23.5 wt%Ni-5 wt% Fe2O3(Mg-Ni-Fe2O3) and 71.5 wt%Mg-23.5 wt%Ni-5 wt% Fe2O3 (spray conversion) (Mg-Ni-scFe2O3), 71.5 wt%Mg -23.5 wt%Ni-5 wt% Fe (Mg-Ni-Fe) and 80 wt%Mg-13.33 wt%Ni-6.67 wt%Fe (Mg-13Ni-7Fe) were prepared by reactive mechanical grinding. Mg-13Ni-7Fe has the highest hydriding and dehydriding rates. After hydriding-dehydriding cycling, all the samples contain the Mg2Ni phase. The samples with Fe2O3and Fe2O3(spray conversion) as starting materials contain the Mg(OH)2 phase after hydriding-dehydriding cycling as well as after reactive mechanical grinding. Mg-Ni-Fe and Mg-13Ni-7Fe contain the MgH2 phase after reactive mechanical grinding. Phases, space groups, cell parameters, contents and crystallite sizes were analyzed by Full Pattern Matching Refinement program, one of the Rietveld analysis programs, from the XRD powder patterns of Mg-Ni-scFe2O3 after reactive mechanical grinding and after hydriding-dehydriding cycling. The MgH2 phase formed in the Mg-Ni-Fe and Mg-13Ni-7Fe mixtures after reactive mechanical grinding is considered to help the pulverization of the materials during reactive mechanical grinding, leading to the high hydriding and dehydriding rates of these mixtures.

      • KCI등재

        Improvement of Hydrogen-Storage Properties of MgH2 by Addition of Ni and Ti via Reactive Mechanical Grinding and a Rate-Controlling Step in Its Dehydriding Reaction

        송명엽,곽영준,Seong Ho Lee,박혜령,Byoung-Goan Kim 대한금속·재료학회 2013 METALS AND MATERIALS International Vol.19 No.4

        In a shift from prior work, MgH2, instead of Mg, was used as a starting material in this work. A sample with a composition of 86 wt% MgH2-10 wt% Ni-4 wt% Ti was prepared by reactive mechanical grinding. Activation of the sample was completed after the first hydriding cycle. The effects of reactive mechanical grinding of Mg with Ni and Ti were discussed. The formation of Mg2Ni increased the hydriding and dehydriding rates of the sample. The addition of Ti increased the hydriding rate and greatly increased the dehydriding rate of the sample. The titanium hydride, TiH1.924, was formed during reactive mechanical grinding. This titanium hydride, which is brittle, is thought to help the mixture pulverized by being pulverized during reactive mechanical grinding and further to prevent agglomeration of the magnesium by staying as a hydride among Mg particles. A rate-controlling step for the dehydriding reaction of the hydrided MgH2-10Ni-4Ti was analyzed by using a spherical moving boundary model on an assumption that particles have a spherical shape with a uniform diameter.

      • KCI등재

        Hydrogenation Reaction of Mg-Based Alloys Fabricated by Rapid Solidification

        송명엽,권성남,Daniel R. Mumm,박혜령 대한금속·재료학회 2013 METALS AND MATERIALS International Vol.19 No.2

        Mg-23.5wt%Ni-xwt%Cu (x=2.5, 5 and 7.5) alloys for hydrogen storage were prepared by melt spinning and crystallization heat treatment. The alloys were ground by a planetary ball mill for 2 h in order to obtain a fine powder. The Mg-23.5Ni-5Cu alloy had crystalline Mg and Mg2Ni phases. Mg-23.5Ni-5Cu had an effective hydrogen capacity of near 5 wt%. The activated Mg-23.5Ni-5Cu alloy absorbed 4.50 and 4.84 wt%H at 573K under 12 bar H2 for 10 and 60 min, respectively, and desorbed 3. 21 and 4.81 wt%H at 573K under 1.0 bar H2 for 10 and 30 min, respectively. The activated Mg-23.5Ni-5Cu alloy showed a quite high hydriding rate like Mg-10Fe2O3, and higher dehydriding rates than the activated Mg-xFe2O3-yNi. This likely resulted because the melting before melt spinning process has led to the homogeneous distribution of Ni and Cu in the melted Mg, and the Mg-23.5Ni-5Cu alloy has a larger amount of the Mg2Ni phase than the Mg-xFe2O3-yNi alloy.

      • KCI등재

        Characterization of a Magnesium-Based Alloy After Hydriding-Dehydriding Cycling (n=1-150)

        송명엽,권성남,박혜령,Daniel R. Mumm 대한금속·재료학회 2013 METALS AND MATERIALS International Vol.19 No.5

        The cycling performance of Mg-15 wt% Ni-5 wt% Fe2O3 alloy (named Mg-15Ni-5Fe2O3) was investigated by measuring the absorbed hydrogen quantity as a function of the number of cycles and by examining the variations in the phases and microstructures with cycling. The sample was hydriding-dehydriding cycled 150 times. The absorbed hydrogen quantity decreased as the number of cycles increased from the second to the 150th cycle. The Ha value varied almost linearly with the number of cycles. The maintainability of the absorbed hydrogen quantity was 73.8%, and the degradation rate was 0.007 wt%/cycle for the hydriding reaction time of 60 min. After the 9th hydriding-dehydriding cycle, Mg, Mg2Ni, MgO, and Fe were observed. After 150 cycles, the quantity of the MgO increased. The phases were analyzed using MDI JADE 6.5, a software system designed for XRD powder pattern processing, from the XRD pattern of the Mg-15Ni-5Fe2O3 alloy after the 9th hydriding-dehydriding cycle. The crystallite size and strain of the Mg were then estimated using the Williamson-Hall technique.

      • KCI등재

        Cycling Performance of LiNi1-y M yO2 (M=Ni, Ga, Al and/or Ti) Synthesized by Wet Milling and Solid-State Method

        송명엽,Daniel R. Mumm,Chan Kee Park,박혜령 대한금속·재료학회 2012 METALS AND MATERIALS International Vol.18 No.3

        The LiNi1-y MyO2 specimens with compositions of LiNiO2, LiNi0.975Ga0.025O2, LiNi0.975Al0.025O2, LiNi0.995Ti0.005O2, and LiNi0.990Al0.005Ti0.005O2 were synthesized by wet milling and a solid-state reaction method. Among all the specimens, LiNi0.990Al0.005Ti0.005O2 has the largest first discharge capacity of 196.3 mAh/g at a rate of 0.1 C. At n=50, LiNiO2 has the largest discharge capacity of 126.7 mAh/g. LiNiO2 has the best cycling performance, its degradation rate of discharge capacity being 0.73 mAh/g/cycle. LiNi0.975Al0.025O2shows the lowest decrease rate of the first discharge capacity with C rate. An equation describing the vari-ation of the discharge capacity with the number of charge-discharge cycles, n, is obtained. The William-son-Hall method is applied to calculate the crystallite size and the strain of the samples before and after charge-discharge cycling.

      • KCI등재

        Hydrogen Storage Properties of a Ni, Fe and Ti-Added Mg-Based Alloy

        송명엽,권성남,홍성현,박혜령 대한금속·재료학회 2012 METALS AND MATERIALS International Vol.18 No.2

        Mg-5wt%Ni-2.5wt%Fe-2.5wt%Ti (referred to as Mg-5Ni-2.5Fe-2.5Ti) hydrogen storage material was pre-pared by reactive mechanical grinding, after which the hydrogen absorption and desorption kinetics were investigated using a Sievert-type volumetric apparatus. A nanocrystalline Mg-5Ni-2.5Fe-2.5Ti sample was prepared by reactive mechanical grinding and hydriding-dehydriding cycling. Analysis by the Williamson-Hall method from an XRD pattern of this sample after 10 hydriding-dehydriding cycles showed that the crystallite size of Mg was 37.0 nm and that its strain was 0.0407 %. The activation of Mg-5Ni-2.5Fe-2.5Ti was completed after three hydriding-dehydriding cycles. The prepared Mg-5Ni-2.5Fe-2.5Ti sample had an effective hydrogen-storage capacity near 5 wt% H. The activated Mg-5Ni-2.5Fe-2.5Ti sample absorbed 4.37 and 4.90 wt% H for 5 and 60 min, respectively, at 593K under 12 bar H2, and desorbed 1.69, 3.81,and 4.85 wt% H for 5, 10 and 60 min, respectively, at 593K under 1.0 bar H2.

      • KCI등재후보
      • KCI등재

        Hydrogen storage properties of pure Mg

        송명엽,곽영준,이성호,박혜령 대한금속·재료학회 2014 대한금속·재료학회지 Vol.52 No.4

        The hydrogen storage properties of pure Mg are investigated at 573 K under 12 bar H2. In addition,in order to increase the hydriding and dehydriding rates of pure Mg, it is ground under hydrogen (reactivemechanical grinding, RMG), and its hydrogen storage properties are investigated. The pure Mg absorbshydrogen very slowly. At n = 1, the pure Mg absorbs 0.05 wt.% H for 5 min, 0.08 wt.% H for 10 min, and0.29 wt.% H for 60 min at 573 K under 12 bar H2. The hydriding rate decreases as the number of cyclesincreases from n = 7. At n = 7, the pure Mg absorbs 0.96 wt.% H for 5 min, 1.29 wt.% H for 10 min, and2.20 wt.% H for 60 min. At n = 1, the pure Mg after RMG does not absorb hydrogen. The hydriding rate of pureMg after RMG increases as the number of cycles increases from n = 1 to n = 11. The pure Mg after RMGabsorbs 1.91 wt.% H for 5 min, 2.61 wt.% H for 10 min, and 3.65 wt.% H for 60 min at n = 11. The reactivemechanical grinding of the pure Mg and the hydriding-dehydriding cycling of the pure Mg after RMG arebelieved to create defects on the surface and in the interior of Mg particles and to form cracks in Mgparticles.

      • KCI등재

        Hydrogen Uptake and Release Characteristics of Mg-xTaF5-xVCl3 (x=1.25, 2.5, and 5)

        송명엽,곽영준 대한금속·재료학회 2018 대한금속·재료학회지 Vol.56 No.8

        TaF5 and VCl3 were chosen as additives to enhance the hydrogen uptake and release rates of Mg. The total content of the additives was not more than 10 wt% since too high content reduces the fraction of Mg and thus the hydrogen storage capacity of the alloys. Samples with compositions of Mg-x wt% TaF5-x wt% VCl3 (x=1.25, 2.5, and 5) were prepared by reactive mechanical grinding. The temperatures at which the asmilled Mg-xTaF5-xVCl3 (x=1.25, 2.5, and 5) began to release hydrogen quite rapidly were 538, 613, and 642 K, respectively. Activation of the samples was not needed. In the first cycle (n=1), Mg-2.5TaF5-2.5VCl3 had quite a high effective hydrogen storage capacity (the amount of hydrogen absorbed for 60 min) of 5.86 wt%. Among the three samples, Mg-1.25TaF5-1.25VCl3 had the best hydrogen release properties. In n=4, Mg-1.25TaF5- 1.25VCl3 had the largest quantity of hydrogen released for 60 min at 593 K in 1.0 bar H2, releasing 0.23 wt% H for 5 min, 0.34 wt% H for 10 min, and 3.31 wt% H for 60 min. After hydrogen uptake-release cycling, Mg- 1.25TaF5-1.25VCl3 had the smallest particle size. In n=5, Mg-1.25TaF5-1.25VCl3 released 2.01 wt% H for 5 min, 3.78 wt% H for 10 min, and 4.89 wt% H for 60 min at 623 K in 1.0 bar H2.

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